How to create a prioritized list view, maybe with a formula field?

We have a challenge where we would like high priority leads to be at the top of our list views and lower priority leads at the bottom. We use a field with a picklist to say if value 'x" then put priority number 4 [on a 1-10 scale] in the "Lead Prioritization" number field. Then we can simply sort by that field.

What is the easiest way to accoplish this? Formula field? Workflow rule?

Thanks all!